Thanks guys. I did a little more this afternoon concentrating on finishing off the nose area and wings. More chipping was done down to the base colours and I also tried to tone down the desert camo on the spine by over-spraying both colours with thinned down XF-88, since this area will be exposed. It still shows up very bright in the shop lighting.
The next applications on the rear of the fuselage are being run through my brain as we speak. I'm trying to apply logic where none may have existed at the time in trying to reconcile how the blue was and wasn't applied. Here's my thought process, much of it being conjecture:
BR301 arrives on board USS WASP in the then tropical scheme of Mid Stone/Dark Earth uppers and Sky Blue undersides
Orders are received resulting in all Spitfires on WASP having to receive a "Sea Scheme" camouflage
WASP is not a floating paint shop so orders are carried out to the extent reasonably possible with limited time, space, and materials.
BR301 is one of the last batch to be painted and receives dark blue uppers, probably thinly applied by brush. Wings are painted whilst standing on them and blue is applied around the existing roundels. Cowls can be painted after removal and are then replaced when paint is dry so the nose area appears darker than other areas.
Rear fuselage takes more time as the s/n and roundels need to be maintained. Time is running out so they say F! it and just paint blue patches before and after the roundels where the ferry markings have to go (3 or 4 plus a letter for Operation Bowery flights). The vertical stab was easy and managed to get the blue paint.
Ferry markings are applied to the blue patches and the plane makes it to Malta where 601 squadron removes or paints over the white ferry marks and applies the "UF-S" markings in white. The UF is to the left of the roundel on each side (my take is that the trace of the top left corner of the U can still be seen faded in the reference pic).
BR301 is transferred to 249 Squadron and retains the UF-S code for ops until at least July 24, 1942.
Between July 24 and 27, 1942, the "UF" is finally replaced with the 249 Squadron code "T" by painting over the "UF" with thin dark blue paint and applying the letter T in Medium Sea Grey. The white S is retained.
BR301 is damaged beyond repair 2 days later.
Unless someone can shoot a proven hole in my theory, that's what I'm going with. Now I have to get the sequence of paint and decals right.